The present invention relates to a conduction-breaking device that breaks conduction between two devices constituting an electric circuit by cutting a conductive body extending between the devices.
Some electric circuits are provided with a conduction-breaking device for breaking conduction between devices by being activated when a malfunction occurs in a device in the electric circuit or in a system on which the electric circuit is mounted. As one form of such conduction-breaking devices, Japanese Laid-Open Patent Publication No. 2012-138286 discloses a conduction-breaking device, which includes a conductive body, an arc-extinguishing chamber, a gas generator, and a cutting member.
The conductive body includes an elongated plate-shaped cuttable portion and is arranged between devices that constitute an electric circuit. The arc-extinguishing chamber has a fixed blade and is provided on one side of the cuttable portion in the thickness direction. The gas generator is arranged on the opposite side of the cuttable portion from the arc-extinguishing chamber with respect to the thickness direction of the cuttable. The cutting member is arranged between the cuttable portion and the gas generator and includes a movable blade. The movable blade cooperates with the fixed blade to cut the cuttable portion.
With the configuration of the above described conduction-breaking device, when the gas generator generates gas while the conductive body is carrying a current, the cutting member receives the pressure of the gas and is moved toward the arc-extinguishing chamber. As the cutting member moves, the cuttable portion receives a shearing force generated by the fixed blade and movable blade, which cuts the cuttable portion. Accordingly, the conduction between the devices is broken.
When the conduction-breaking device is activated and the conductive body in a current-carrying state is cut, a pair of cut ends are formed in the conductive body. An arc may be generated due to the potential difference between the pair of cut ends. An arc is a phenomenon in which insulation of gas present between the cut ends is overcome and a current flows between the cut ends.
When an arc is generated, the cut ends are electrically connected to each other. In this case, although being physically cut, the conduction is not broken, and the conductive body may remain in a current-carrying state. Further, the arc may melt the conductive body and its surrounding plastic members.
In this regard, the conduction-breaking device of Japanese Laid-Open Patent Publication No. 2012-138286 has two fixed blades, which are arranged in the arc-extinguishing chamber and separated from each other in the longitudinal direction of the cuttable portion. The cutting member has two movable blades at two positions that are separated from each other in the longitudinal direction of the cuttable portion. Thus, as the cutting member moves, the cuttable portion receives shearing force generated by the fixed blades and movable blades at two positions. The shearing force cuts the cuttable portion at the two positions. When the cuttable portion is cut at the two positions, the cuttable portion forms a separated piece, which is separated from the electric circuit through the cutting action, and two remaining portions, which remain connected to the electric circuit. Accordingly, the conduction between the devices is broken. Since the cuttable portion is cut at two positions, the electric resistance is increased. Therefore, the voltage required to generate and maintain an arc is increased. That is, an arc is unlikely to be generated.
However, in the conduction-breaking device of Japanese Laid-Open Patent Publication No. 2012-138286, the separated piece is formed to have a flat shape like the shape prior to the cutting action. Thus, the distance between each cut end of the separated piece and the cut end of the corresponding remaining portion is short. The device of the publication is therefore susceptible to improvement in terms of attenuation of arcs.